In the United States, the year is 2020 AD, but, in what other countries is the year different? Why?

An Ethiopian year is comprised of 13 months, and is seven years behind the Gregorian calendar. Ethiopians celebrated the new millennium on September 11, 2007.

Explanation:

Why they are so late is because they have 13 months in a year.

the correct answer is the following is a list of inventions made in the medieval islamic world, especially during the "islamic golden age" (8th to 13th centuries),[1][2] as well as the late medieval period, especially in the emirate of granada and the ottoman empire.

science and technology in the islamic world adopted and preserved knowledge and technologies from contemporary and earlier civilizations, including persia, india, china, and greece-roman antiquity, while making a number of improvements and innovations.